This tap exists to support macOS FUSE-related software that have been dropped from Homebrew core.
brew install gromgit/fuse/<formula>
Probably because I haven't gotten around to putting it in yet. If you need it, file an issue and I'll see what can be done.
Maybe I just haven't gotten around to updating it yet, but a significant subset simply can't be updated until MacFUSE supports version 3 of the FUSE API. Read any Caveats that appear during installation for important details.
brew help, man brew or check Homebrew's documentation.